Pelorism
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Pelorism is the term, said to be first used by
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
, for the formation of 'peloric flowers' which botanically is the abnormal production of radially symmetrical (
actinomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
) flowers in a species that usually produces bilaterally symmetrical (
zygomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spir ...
) flowers. These flowers are spontaneous
floral symmetry Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
mutants. The term epanody is also applied to this phenomenon. Bilaterally symmetrical (zygomorphic) flowers are known to have evolved several times from radially symmetrical (actinomorphic) flowers, these changes being linked to increasing specialisation in pollinators.


History

Pelorism has been of interest since a five-spurred variety of the common toad-flax (''
Linaria vulgaris ''Linaria vulgaris'', the common toadflax,Blamey, M. & Grey-Wilson, C. (1989). ''Flora of Britain and Northern Europe''. yellow toadflax or butter-and-eggs, is a species of flowering plant in the family Plantaginaceae, native to Europe, Siberia ...
'' L.) was first discovered in 1742 by a young
Uppsala Uppsala ( ; ; archaically spelled ''Upsala'') is the capital of Uppsala County and the List of urban areas in Sweden by population, fourth-largest city in Sweden, after Stockholm, Gothenburg, and Malmö. It had 177,074 inhabitants in 2019. Loc ...
botanist on an island in the
Stockholm Stockholm (; ) is the Capital city, capital and List of urban areas in Sweden by population, most populous city of Sweden, as well as the List of urban areas in the Nordic countries, largest urban area in the Nordic countries. Approximately ...
archipelago and then in 1744 described by
Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
. The mutant, spreading vegetatively, had five spurs rather than the usual one; however, the rest of the plant was normal. Linnaeus found that this variety was contrary to his concept that genera and species had universally arisen through an act of "original creation and remained unchanged since then". Linnaeus called this type of mutant a 'Peloria', the Greek for 'monster' or 'prodigy', because of the huge implications for the then current belief that species were immutable. He wrote that "This is certainly no less remarkable than if a cow were to give birth to a calf with a wolf's head." The peloric plant fascinated Linnaeus to the extent that he grew it at his summer residence in Hammarby and his explanation for it was that a toad-flax had been pollinated by another species.
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
,
Charles Victor Naudin Charles Victor Naudin (14 August 1815 in Autun – 19 March 1899 in Antibes) was a French naturalist and botanist. Biography Naudin studied at Bailleul-sur-Thérain in 1825, at Limoux, and at the University of Montpellier from which he gradua ...
,
Johann Wolfgang von Goethe Johann Wolfgang (von) Goethe (28 August 1749 – 22 March 1832) was a German polymath who is widely regarded as the most influential writer in the German language. His work has had a wide-ranging influence on Western literature, literary, Polit ...
and
Hugo de Vries Hugo Marie de Vries (; 16 February 1848 – 21 May 1935) was a Dutch botanist and one of the first geneticists. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while apparently unaware of ...
amongst others analysed and wrote about this significant mutation. The botanist Thomas Fairchild corresponded with
Carl Linnæus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
. Fairchild scientifically produced an
artificial hybrid In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different varieties, subspecies, species or genera through sexual reproduction. Generally, it means that each cell has genetic material from two dif ...
, ''
Dianthus caryophyllus ''Dianthus caryophyllus'' ( ), commonly known as carnation or clove pink, is a species of '' Dianthus'' native to the Mediterranean region. Its exact natural range is uncertain due to extensive cultivation over the last 2,000 years. Carnations ...
'' x '' barbatus'' in 1717 that became known as 'Fairchild's Mule', a cross between a
sweet william Sweet William may refer to: * '' Dianthus barbatus'', a species of flowering plant * '' Mustelus antarcticus,'' a species of shark * ''Sweet William'' (novel), a 1975 novel by Beryl Bainbridge * ''Sweet William'' (film), a 1980 British drama fil ...
and a
carnation ''Dianthus caryophyllus'' ( ), commonly known as carnation or clove pink, is a species of ''Dianthus'' native to the Mediterranean Basin, Mediterranean region. Its exact natural range is uncertain due to extensive cultivation over the last 2,00 ...
. The production of hybrids further undermined the belief that species as created by God were immutable.


Appearance and causation

It is notable in foxgloves that the terminal flower more frequently develops peloric features than lateral flowers and this has had been put down to terminal buds having a greater supply of sap. Charles Darwin took a particular interest in peloric flowers, growing and
cross-pollinating Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or butterflies; birds ...
antirrhinums himself, as he saw the phenomenon as suggestive of a partial reversion to a past or ancestral type. Peloric forms quite commonly appear as random mutations in several orchid species in nature and this is genetically controlled, although the expression can be influenced by both environmental changes and by stresses. The occurrence is unstable and the same plant may exhibit normally on the next flowering. In more highly evolved flowers such as orchids the details of pelorism may appear more complex with characteristics such as the two lateral petals replaced by two additional labella, the labellum replaced by an additional lateral petals in semipeloria or pseudopeloria where the modified labellum is less distinctively altered, however it is still distinguishable from the lateral petals and this confers a degree of zygomorphy upon the petal whorl. Although the production of peloric flowers has been shown to generally follow standard Mendelian inheritance, this is not fixed and had been linked to the inability of a plant to produce normal internodes, this failure resulting in the fusion of flower buds, giving
actinomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
flowers. Foxglove plants show the terminal peloric bud flowering first followed by the more normal buds flowering below, the reverse of the normal flowering pattern, the terminal flowers withering first. The CYCLOIDEA (CYC) gene controls floral symmetry and peloric
antirrhinum ''Antirrhinum'' is a genus of plants in the Plantaginaceae family, commonly known as dragon flowers or snapdragons because of the flowers' fancied resemblance to the face of a dragon that opens and closes its mouth when laterally squeezed. They ...
s have been artificially induced by this gene being knocking out.


Etymology

Peloria derives from both new Latin and from the Greek word , meaning 'monstrous'.


Examples

Pelorism is found in several
orchid Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Orchids are cosmopolitan plants that are found in almost every habitat on Eart ...
species, such as ''
Phalaenopsis ''Phalaenopsis'' (), also known as moth orchids, is a genus of about seventy species of plants in the family Orchidaceae. Orchids in this genus are monopodial epiphytes or lithophytes with long, coarse roots, short, leafy stems and long-lastin ...
'' it is demonstrated by flowers with abnormal numbers of petals or lips as a genetic trait, the expression of which is environmentally influenced and may appear random. It is widely noted in the mint family and species such as ''
Digitalis purpurea ''Digitalis purpurea'', the foxglove or common foxglove, is a toxic species of flowering plant in the plantain family Plantaginaceae, native to and widespread throughout most of temperate Europe. It has also naturalized in parts of North Ame ...
'', gloxinia, ''
Antirrhinum majus ''Antirrhinum majus'', the common snapdragon (often – especially in horticulture – simply "snapdragon"), is a species of flowering plant belonging to the genus ''Antirrhinum''. The plant was placed in the family Plantaginaceae following a r ...
'', ''
Pelargonium ''Pelargonium'' () is a genus of flowering plants that includes about 280 species of perennial plant, perennials, succulent plant, succulents, and shrubs, common name, commonly called geraniums, pelargoniums, or storksbills. ''Geranium'' is also ...
'', and auricula. Because peloric flowers are larger and arguably more attractive than normal flowers plants such as cultivars of the gloxinia (''Sinningia speciosa'') have been deliberately bred to have peloric flowers.


See also

*
Floral symmetry Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...


References


External links


Peloric Foxglove flowers


Further reading

* * * * {{cite journal , author1=Neal P. R. , author2=Dafni A. , author3=Giurfa M. , title=Floral symmetry and its role in plant-pollinator systems: terminology, distribution, and hypotheses , journal=Annu Rev Ecol Syst , volume=29 , pages=345–373 , year=1998 , jstor=221712 , doi=10.1146/annurev.ecolsys.29.1.345, bibcode=1998AnRES..29..345N Plant morphology